According to the text:

• Scoliodon (Dog fish) belongs to Class Chondrichthyes, which has a two-chambered heart .
• Hippocampus (Sea horse) belongs to Class Osteichthyes, which has a two-chambered heart .
• Pteropus (Flying fox) belongs to Class Mammalia, which has a four-chambered heart , .
• Chelone (Turtle) belongs to Class Reptilia. The text states that in reptiles, the heart is usually three-chambered (except in crocodiles) .